Electricity is transmitted from generating stations to electrically powered devices by metal conductors. The preferred metal is copper because of its excellent conductivity and relatively low price. The metal conductors are known as wire when they consist of a relatively small diameter single strand and are known as cable when they consist of multiple strands wound together. Both wire and cable are commonly coated with a flexible plastic insulator. Most electrically-powered devices are connected with at least three separate wires or cables, one is known as the positive, one is known as the negative or neutral, and one is a ground cable whose purpose is to carry the current to the Earth in the event of a malfunction.
On an atomic level, the flow of electricity is the movement of electrons. The movement generates friction and the friction generates heat. The diameter of the conductor must be large enough to prevent the generation of excessive heat. The minimum safe diameter of the conductor is thus a function of the voltage and current of the electricity. For example, 12 gauge (American wire gauge) copper wiring having a diameter of about 0.08 inches (about 3.2 mm) is the minimum for many residential circuits (120 volts and 20 amperes) whereas copper cable for industrial use is often one inch (about 2.5 cm) or more in diameter. Larger diameter wire and cable are typically placed onto spools at the point of manufacture and are unrolled from the spools at the point of installation.
For residential and commercial buildings, three insulated wires or cables within a plastic case are commonly used for the electrical system. For industrial applications, the wires or cables are usually installed within a metal or plastic conduit. The conduit provides additional protection and safety. The installation process typically requires the wires or cables to be unrolled from spools and then pulled through the conduit.
Pulling large diameter cables through a conduit is difficult because the cables tend to bind with each other and to rub against the inside wall of the conduit. While pulling through a straight conduit can be difficult, pulling through curved sections of conduit is even more difficult. Electricians commonly coat the cables with a solution of soapy water or other lubricant to reduce friction as they are pulled through a conduit.
A variety of conduit inserts have been disclosed. For example, Conti et al., U.S. Pat. No. 5,027,864, Jul. 2, 1991; Allen, U.S. Pat. No. 6,262,371, Jul. 17, 2001; Morris, U.S. Pat. No. 7,319,802, Jan. 15, 2008; and Washburn, U.S. Pat. Appln. Publn. No. 2007/0130760, Jun. 14, 2007, disclose conduit inserts that run the entire length of the conduit and separate individual cables within the conduit. These conduit inserts require the cables to be fed simultaneously into the inserts. It is very difficult to precisely align and then feed three or more bulky cables simultaneously into a conduit insert.
A variety of cable supports and protectors have also been disclosed. For example, Henry, U.S. Pat. No. D436,578, Jan. 23, 2001; Wakamatsu, U.S. Pat. No. 5,780,773, Jul. 14, 1998; Ayoub, U.S. Pat. No. 7,633,010, Dec. 15, 2009; and Symons, U.S. Pat. No. D648,685, Nov. 15, 2011, disclose cable supports and protectors that separate cables. However, these cable supports and protectors are not suitable for use in conduits.
A variety of circular and disc-shaped guides for cables and other flexible linear materials have also been disclosed. For example, Suhr, U.S. Pat. No. 5,027,478, Jul. 2, 1991; Heacox, U.S. Pat. No. 6,552,270, Apr. 22, 2003; Denton, U.S. Pat. No. 6,710,249, Mar. 23, 2004; and Kim et al., U.S. Pat. No. D601,879, Oct. 13, 2009, disclose guides having outwardly facing recesses arranged around a center. These guides are not suitable for use in conduits.
Accordingly, there is a demand for an improved cable guide without moving parts that enables multiple cables to be separated on a spool or in a conduit at desired intervals and that can be placed onto the cables at the point of manufacture or at the job site without requiring the cables to be fed into and through the guide.